Currently, the traction transformer is commonly used as a power equipment in the electrified railway field, which characteristic long time of no-load operation (the traction transformer is almost no-load in the trains gap period), high overload capacity, and more times of short-circuit. Conventional traction transformers are used the laminated iron core, which inner and outer coils are sequentially fitted over the iron core. The laminated iron core is made of the laminated silicon steel. The air gap, which has high value of magnetic reluctance, is formed in the butt joint of the silicon steel, so that no-load losses and no-load current is increased, and the noise is relatively larger. The process of cutting and stacking the silicon steel, which also makes the no-load losses increasing, will affect the arrangement of magnetic domains. A gap should be reserved when loop coils are looped, however the gap would decrease the resistance of short-circuit of the coil.